Musical apparatus

ABSTRACT

The present disclosure relates to apparatus for improving the tonal characteristics of a musical instrument in such a manner as to elicit excited responses from professional musicians; and more particularly, it teaches how the disclosed apparatus may be used for improving the tonal characteristics of a guitar. Variations of the apparatus permit the musician to achieve different special effects.

United States Patent 1191 Woods Jan. 14, 1975 MUSICAL APPARATUS3,449,681 6/1969 Hafler 3311/1119 x [76] Inventor: Walter Woods, 124 S.Avenue 63, OTHER PUBLICATIONS L05 g Calif- 90042 E. J. Gately, Jr., TheWonderful World of Integrated Nov. 24 Circuits Audio, June, 36, 8L [21]Appl. No.: 309,153 Primary ExaminerJohn Zazworsky Attorney, Agent, orFirm-Francis X. LoJacono, Sr.

U. l 28 l 7 7, [52] S C 3 6 307/233 322x001 ABSTRACT [51] Int. Cl. H03k1/16 The Present disclosure relates to apparatus for 5 Field f Search H323 7; 330 107 1 9; proving the tonal characteristics of a musicalinstru- 34/ 01 1 444; 307/233 ment in such a manner as to elicit excitedresponses from professional musicians; and more particularly, it 5References Cited teaches how the disclosed apparatus may be used forUNITED STATES PATENTS improving the tonal characteristics of a guitar.Varia- 3 059 190 10/1962 Hafler 330mm X tions of the apparatus permitthe musician to achieve 3:096:488 7/1963 Lomaslcjxix22:22:: 330/107 xdfferem Speclal effects 3,130,374 4/1964 Beres et a1. 330/109 X 23Claims, 12 Drawing Figures lT i f PATENTEI] JAN 1 M975 SHEEI 20F 3MUSICAL APPARATUS BACKGROUND It is well known that a musical instrumentproduces a characteristic range of tones, these depending on a largenumber of different factors in general, a large instrument producingdeeper tones than a smaller instrument. Among the tone-modifying factorsare, for example: the body size; the body shape; the particular mode ofplaying the instrument; and (in string instruments) the string tension,the string size, the type and location of the bridge, the body bracing,the shape and position of the sound holes, etc. Unfortunately, therelation between these various factors is extremely complex, and theirinteractions are not well understood.

Therefore, producing a good musical instrument is a work of art, ofscience, and of skill; and, since only a relatively few really goodinstruments are produced, they are both expensive and highly prized.

In general, a group of qualified musicians will agree upon a goodinstrument; but even so, a particular musician may not be completelysatisfied with a given instrument and the reason for this will beunderstood from the following discussion.

It is well known that a pure note say as produced by a tuning fork maybe technically expressed as a frequency having a given number ofvibrations per second. However, such a pure note known as a fundamentalis not very useful from a musicians point of view, because such amusical note needs a plurality of harmonics or overtones" of higherfrequencies to fill out the note and to produce a tone.

Every different type of instrument e. g., violin, trumpet, etc. producesan individually characteristic combination of tones, i. e., fundamentalsand harmonics. For this reason, it is possible to recognize a tone asoriginating from a violin, and to distinguish a violin tone from atrumpet tone. Furthermore, each individual instrument whether it be aviolin or a trumpet differs somewhat from other instruments of itsclass, because each individual instrument has an individual structurethat causes it to produce an individual combination of fundamentals andharmonics that differs from the combination of fundamentals andharmonics produced by the other instruments of its class.

As a result of these instrument tonal characteristics, each musician isconstantly searching for a musical instrument that sounds right to him;and, while a good instrument generally sounds right to a number ofdifferent musicians, each musician may personally desire a slightlydifferent combination of tones.

For ease of comprehension, the following explanation will be presentedin terms of a guitar; although, it will be later realized that thediscussion and disclosure apply to a wide range of musical instruments,and to other apparatus.

Of late, a much larger share of musical attention is being given to theguitar partly because of the ease with which it may be played, andpartly because a gifted musician is able to produce such a wide range ofmusic thereon. As a result, the guitar now occupies a prominent place inentertainment both as a solo instrument and as part of a musical group.

This trend toward wider use of the guitar has introduced twosimultaneous problems, as follows. First of all, the volume of soundproduced by an acoustical, hollow-body guitar tends to be too smallcompared to the sound volume of other musical instruments. Secondly, thetonal range of the guitar tends to be too limited. It became feasible toincrease the tonal range of the guitar by introducing a so-called familyof guitars including bass guitars, intermediate-range guitars, tenorguitars, guitars with different numbers of strings, etc.

In order to produce improved bass tones, the bass guitar tended to growin size with each new generation thereof, so that eventually the bassguitar became so large as to be unwieldy. It turns out that both ofthese problems (volume and size) may be simultaneously solved by arelatively simple solution, namely, by the use of an electronic soundsystem comprising a microphone, an electronic amplifier, and a loudspeaker the composite sound system increasing the volume, anddisproportionately amplifying the bass notes.

One disadvantage of this electronic sound arrangement was that itsmicrophone was unsightly. Another disadvantage was that it tended tolimit the musician s on-stage mobility. Still another, more important,disadvantage was that the musician now tended to be limited by thecharacteristics of the electronic sound system; so that, often, theaudience did not hear the tones that the musician felt were desirable.

Fortunately, with the advent of transistors and new materials, it becamepossible to build the amplifiers and the microphones (now known aspick-ups) small enough so that they could fit into the hollow body ofthe guitar; although, the more powerful amplifiers are still placed onstage along with the musician.

It may thus be understood that despite the miniaturized sound system amusician, having found a musical instrument that comes close tosatisfying his personal tonal requirements, is greatly disturbed when anelectronic sound system over which he has no control distorts the tonefrom his musical instrument.

Due to the introduction of these electronic, transistorized amplifiers,it now became feasible to have the electronic amplifier rather than theguitar produce the desired bass tones; so that it was no longernecessary to build large, hollow-body, acoustical, bass guitars. As aresult, the newest type of guitar is the socalled solid-body guitar, asillustrated in FIG. 1. This type of guitar has a body that instead ofbeing hollow is a block of wood about two inches thick, and of asuitable size and shape, a portion of the solid body being hollowed outto accommodate the necessary electronic components. Thus, with asuitable, miniaturized, electronic circuit, the solid-body guitar isable to minimize the need for the prior-art, large, hollow-body,acoustical, bass guitar. However, most professional musicians complainedthat the sound from these electronic guitars was dead, dull, orsimilarly described.

Thus, it becomes desirable to provide apparatus that improves the soundof a musical instrument.

OBJECTIVES AND DRAWINGS FIG. 1 shows a pictorial view of a guitar;

FIGS. 2 7 show various waveforms representative of response curves thatmay be attained by the use of the subject apparatus;

FIGS. 8 and 9 show circuitry for the subject apparatus;

FIGS. and 11 show families of waveforms representative of responsecurves that may be attained by the use of the subject apparatus;

FIG. 12 shows a pictorial view of how the subject apparatus may bepackaged.

SYNOPSIS Broadly speaking, the present disclosure teaches that a novel,live sound is produced by selectively amplifying and/or attenuating thefundamental tones and their harmonics in a specialized manner thatproduces a sharp differentiation between the fundamental frequencies andtheir harmonics. This result is attained, producing a lower range offrequencies that has a sharp roll-of portion, an upper range offrequencies that has a sharp roll-on portion, and a mid-range offrequencies that sharply separates the lower range of frequencies fromthe upper range of frequencies.

The present disclosure indicates that special sound effects are oftendesired for specific purposes, and that special conditions are oftenrequired for practicing; and it teaches how the apparatus may bemodified to achieve such special sounds and conditions.

Basic Concept I have discovered a new, previously-unknown concept thatcauses a musical instrument, such as a guitar, to produce a sound thatthrills professional musicians, the comments being such as brilliant,live, and the like. Moreover, my inventive concept permits eachindividual musician to modify the sound in such a way that he ispersonally pleased. Furthermore, my inventive concept may be used with arelatively cheaplymade guitar, and may even be used to cause a giveninstrument to act selectively as a bass guitar, as a midrange guitar, oras a tenor guitar.

Originally, it was believed that, in order to produce satisfactorybass-guitar sounds, it was merely necessary to have an electronic soundsystem capable of amplifying the bass notes. However, this arrangementhas not proved satisfactory.

My basic concept, on the contrary, not only amplifies the bass notes,but also strongly aamplifies the treble notes especially thelower-frequency harmonics and, when desired, may even amplify orattenuate the intermediate notes. The resultant combination offundamentals and harmonics produces bass sounds having tonal colors thatfar surpass those produced previously.

Response Curve of FIG. 2

The present inventive concept will be better from FIG. 2, which shows aresponse curve 10 that depicts the amount of amplication measured indecibels (dB), and indicated to be increasing in a verticallyupwarddirection for each frequency (indicated to be increasing in a rightwarddirection). The audio frequency spectrum ranges, typically, from aboutvibrations per second (Hertz, or B2) to about 20,000 Hz. As indicated inFIG. 2, a lower bass range of frequencies extending from about 20 Hz toabout 400 Hz is amplified in such a manner that thelower-rangeamplification waveform 11 has a steep roll-of portion 12 thatterminates or anchors at a given anchoring frequency such as 400 Hz;although, another anchoring frequency may be used. In general, thefrequencies below the anchoring frequency may be considered to be theabove-discussed fundamentals.

FIG. 2 also indicates that an upper treble range of frequenciesextending upwards of the anchoring frequency is amplified in such amanner that the upperrange-amplification waveform 13 has a steep roll-onportion 14 that is also anchored at substantially the anchoringfrequency. In general, the frequencies above the anchoring frequency maybe considered to be the harmonics of the various fundamentals.

Thus, as indicated in FIG. 2, the fundamental and harmonic frequenciesare strongly amplified, in order to give them a large enough emplitudeto be incorporated into the overall sound of the guitar.

It should be noted, however, that since relatively few of thehigh-frequency, treble notes are produced in a bass guitar, therelatively-high amplification of the treble notes does not drown out thebass notes. Thus, the bass notes still predominate.

Attention is directed, in FIG. 2, to the notch" 15 between the roll-offportion 12 and the roll-on portion 14, notch 15 in the response curve 10indicating that there is a mid-range of frequencies that receivesminimal amplification. It has been found desirable to have the notch 15of such configuration that it permits sharply reduced amplification ofthe fundamental frequencies within two octaves below the anchoringfrequency, and permits sharp amplification of the harmonics within twooctaves above the anchoring frequency the bassrange wavefore 11 and thetreble-range waveform 13 flattening out beyond these limits.

It appears that the novel, aural results provided by my invention aredue to the co-action of the steep, rolloff portion 12 and the steep,roll-on portion 14, and to the minimum amplification in the notch 15these factors combining to produce a sharp distinction between thefundamentals and the harmonics.

Response Curve of FIG. 3

There are some musical arrangements wherein a bass guitar is usedprimarily for rhythm and/or background and, therefore, should notproduce treble notes that might intrude upon the melody being played byother instruments. The present invention permits this result to beachieved by producing a response curve that causes the guitar to produceprimarily bass notes, and not produce any appreciable amount of treblenotes.

Such a response curve 16 is shown in FIG. 3, this result being achievedby using the previously-discussed, bass waveform ll but inverting thepreviouslydiscussed, treble waveform 13. In this way, the overallresponse curve 16 of FIG. 3 produces sound containing amplified basstones and attenuated treble tones.

Thus, the present invention permits the output sound of a given bassguitar to be modified to produce a live bass sound or a bass rhythmsound.

Response Curve of FIG. 4

There are times when it may be desirable to amplify a greater range ofbass notes; and the present invention permits this result to be achievedby producing a response curve such as indicated at 17 in FIG. 4. Toproduce such a response curve, the above-discussed, bass waveform 11 isused as explained above, along with a mid-range waveform 18. For reasonsto be discussed later, this mid-range waveform 18 is preferably of sucha configuration that it is an inversion" of the notch 15 between thebass-range, roll-off portion 12 and the treble-range, roll-on portion 14of FIG. 2, having its peak at the anchoring frequency.

The result of using the bass portion 11 and the intermediate portion 18is indicated in FIG. 4, and produces the composite response curve 17that equally amplifies all of the bass tones up to the anchoringfrequency, as indicated by the horizontal bass portion of the responsecurve 17, while gradually attenuating the treble notes.

Response Curve of FIG. 5

In some cases, it is desired that the response curve contain more bassnotes but still fewer treble notes; and FIG. 5 shows a suitable responsecurve 20. In obtaining curve 20, the original bass-range waveform 11 isused in its amplifying mode; the original treble-range waveform 13 isused in its attenuating mode; and the intermediate-range curve 18 isused in its amplifying mode. As indicated by the composite responsecurve 20, the bass notes are equally amplified for an extended bassrange; whereas the treble notes are attenuated sooner and more severelythan by the response curve 17 of FIG. 4.

Response Curve of FIG. 6

There times when it is desirable to equally amplify all of thefrequencies such a situation arising, for example, in a musical groupwhen volume is more desirable than individual tones. FIG. 6 shows aresponse curve 22 that achieves this result. Here, all three rangewaveforms 11, 13 and 18 are used in their amplifying modes; so that thecomposite response curve 22 is substantially flat and horizontalindicating that all of the frequencies are amplified to asubstantially-equal extent. This particular response curve 22 ispossible because the mid-range waveform 18 substantially fills in thenotch 15.

Response Curve of FIG. 7

While the disclosed inventive concept has been presented in terms of abass guitar, it of course has other uses. For example, if the individualwaveforms ll, 13 and 18 are combined as indicated in FIG. 7, they co-actto produce a response curve 24 that attenuates the lower frequencies,and strongly amplifies the higher frequencies.

Thus, the present invention provides a plurality of range waveforms thatmay be selectively combined in amplification and/or attenuating modes toprovide various types of response curves.

THE ELECTRONIC CIRCUITRY The above-described response curves, andothers, may be formed by electronic circuitry such as is shown in FIG.8. For convenience of explanation, the disclosed circuitry will bedivided into several separate stages which, however, cooperate toproduce the desired results.

The Input Network As discussed above, various pick-ups convert theacoustical vibrations of the guitar into electrical signals ofcorresponding frequencies; and, depending upon the design of thepick-ups, some of them produce larger amplitude signals than others. Inorder to accommodate pick-ups of various types, the disclosed electroniccircuit has an input network 30 that has two input jacks (J 1 and J2).When these jacks are not being used, the

jack circuits are short circuited to ground in order to minimizeextraneous noise and the like.

Input jack Jl is adapted to receive signals from a lowamplitude pick-up;and, when a plug from such a lowamplitude pick-up is inserted into jackJ1, resistors R1 and R2 are effectively connected in parallel; so thatthe relatively-low-amplitude, pick-up signals encounter minimalresistance and appear at the output of network 30.

Input jack J2 is adapted to receive signals from a high-amplitudepick-up; and, when a plug from such a high-amplitude pick-up is insertedinto jack J2, resistors R1 and R2 are effectively connected to form avoltage divider; so that about half of the relatively-highamplitudesignal appears at the output of network 30.

Thus, the input network 30 produces a desiredamplitude, output signal,regardless of whether the input signal had a high or low amplitude.

The Voltage Amplifier It so happens that many of the music audienceshave become accustomed to a distortion produced by earlier amplifiersoperating at high gain; and these audiences have come to expect certainmusical selections to contain this distortion. As a result, it becomesdesirable for the musician to be able to produce such a distortion whenhe deems it advisable; and the disclosed electronic circuitry of FIG. 8contains a distortion amplifier 32 for achieving this function.

It may be seen that voltage amplifier 32 has an amplifier All that hastwo inputs, an output, and an internal, feedback circuit that feeds aportion of the output back into the input the feedback being negative inthat it tends to counteract the input.

The voltage amplifier 32 functions as follows. When the slider ofpotentiometer R5 is at its rightmost position, the output signal is feddirectly to ground, so that no signal is applied to subsequentcircuitry. On the other hand, when the slider of the potentiometer R5 isat its leftmost position, the feedback is attenuated by the resistanceof the potentiometer which bypasses RS of FIG. 9, so that the feedbacksignal has very little effectiveness permitting maximal gain of theamplifier.

FIG. 9 shows a typical schematic diagram of amplifier All. As shown, itcomprises a drain resistor RD, a source resistor RS, an emitter resistorRE, a field-effect transistor (FET) QA which has a voltagecharacteristic that resembles the characteristics of prior-art, vacuumtubes, and a bi-polar transistor QB having a characteristic that istypical of a transistor. The circuit of FIG. 9 is such that the negativefeedback assures minimal amplifier gain to preclude overloading; but,when the amplifier is driven hard by placing the potentiometer R5 ofFIG. 8 at its leftmost position, amplifier 32 tends to produce avoltage-type distortion similar to that produced by prior-art, tube-typeamplifiers. In this way, the voltage amplifier 32 acts as a distortioncontrol.

The Fixed, Waveform Generator As was pointed out previously, it isdesirable to produce a bass-range waveform 11 as discussed in connectionwith FIGS. 2 7; and such waveforms may be produced by a fixed,waveform-generating circuitry, indicated at 35 of FIG. 8. This circuitproduces the fixed waveforms 11 and 13 in the following manner.

The Bass Circuitry, Neutral-Switch Setting Directing attention first tothe lower portion of the circuitry indicated at 35, it will be notedthat this circuitry contains a single-pole, three-position switch S1,switch S1 being shown in its neutral setting. In this neutral setting,the circuit operates as follows.

The incoming signal (from the voltage amplifier 32) contains, it will berecalled, a plurality of various fre quencies that correspond to thevarious notes produced by the pick-up of the guitar. The incoming signaltraverses an input path comprising circuit elements R7, R9, C5, R10 andR16; and it is then applied to the input terminal of amplifier A2 whichmay be generally similar to amplifier A1, previously described. Theinput signal is thus amplified by amplifier A2; and appears at theoutput terminal of amplifier A2. A feedback path comprising circuitelements C10, R12, R11, C6, R10, and R16 applies a feedback signal tothe input terminal of amplifier A2.

Typically, R7 equals R12; R9 equals R11; R9 equals 10 X R7; R11 equals10 X R12; C equals C6; R15 provides a resistive path to ground forproper return of the negative input terminal of A2; R16 is forsuppression of radio signals; C9 bypasses the positive input terminal ofamplifier A2 for maximum open-loop gain of A2 throughout theaudio-frequency range; C provides a low-impedance path for output andfeedback signals through the audio-frequency spectrum.

Since corresponding circuit elements of the input path and of thefeedback path are substantially equal, the applied input signal isidentical at all frequencies to the applied feedback signal. Thus, thefixed, waveform-generating circuit 35 has a gain of zero decibels. Forconvenience, this gain is designated as a unity amplification; and isdepicted as a straight horizontal line at zero dB of FIGS. 2 7, thisstraight horizontal line indicating that all of the frequencies areamplified equally.

Digression It is well known that an electronic circuit element known asa capacitor tends to transmit progressively higher frequencies inprogressively greater amounts that is, it is frequency sensitive; andthis characteristic is used in the present circuit.

The Bass Circuit, Boost-Switch Setting When switch S1 is placed in itsleftmost or boost setting, the bass-range waveform 11 is generated asfollows. When switch S1 is at its boost setting it shorts out C5 and R9;so that the effective input path now comprises only R7, Sl, R10, andR16, this being a relatively-low-resistance, resistive(non-frequency-sensitive) path. The feedback path still comprises C10,R12, R11, C6, R10, and R16; so that this feedback paths impedance variesinversely with frequency for signals below 400 Hz. As a result, theinput signal is larger than the feedback signal for frequencies lessthan 400 Hz; and the overall gain of the amplifier A2 is boosted up to20 dB for frequencies less than 100 Hz, as indicated at waveform ll ofFIGS. 2 and 4.

For input frequencies greater than 100 Hz, capacitor C6 exhibits anever-decreasing resistance to the feedback signal; so that, for thesehigher frequencies, progressively larger feedback signals are applied toamplifier A2 in this way, decreasing its overall gain for frequencies inthe e 400 Hz range, and resulting in the roll-off portion 12 of FIGS. 26, which reaches zero dB at the anchoring frequency of about 400 Hz.

In order to achieve an even steeper roll-off portion 12, use is made ofa waveform-shaping network 37 comprising R8 and C8, this shaping networkpermitting the input-signal path and the feedback-signal paths to beequal, resulting in unity gain and a characteristic notch at 400 Hz.

The Bass Circuit, Cut"-Switch Setting When switch S1 is placed in arightmost, or its cut setting", the bass-range waveform 11 is generatedin an inverse from (See FIG. 7), as follows. With switch S1 at its outsetting, it shorts out C6 and R11; so that the effective feedback pathnow comprises only C10, R12, S1, R10, and R16 this being arelatively-lowresistance, non-frequency-sensitive path. The input pathstill comprises R7, R9, C5, R10, and R16; so that the input path has aprogressively-larger impedance for frequencies below 400 Hz than thefeedback path. As a result, the applied feedback signal is larger thanthe applied input signal; and the overall gain of amplifier A2 isseverely reduced, or cut, for frequencies up to about 100 Hz.

For frequencies greater than about 100 Hz, capacitor C5 of theinput-signal path exhibits an ever-decreasingimpedance to the inputsignal; so that, for these higher frequencies, progressively-largerinput signals are applied to the amplifier A2 in this way, increasingits overall gain for frequencies in the 100 400 Hz range, and resultingin the inverted roll-off portion 12 of FIG. 7.

In order to maintain the steeper roll-off portion 12, waveform-shapingnetwork 37 permits unity gain at 400 Hz, as discussed previously.

In actuality, the inverted, bass-range waveform 11 of FIG. 7 is obtainedby minimal amplification; but by electronically repositioning the zerodB base line the inverted, negative-going, bass-range waveform may beconsidered to be negatively amplified, or attenuated. It will be notedthat the roll-off portion 18 is still substantially anchored at theanchoring frequency.

The Treble Waveform, Neutral-Switch Setting Referring again to thefixed, waveform generator 35 of FIG. 8, it will be noted that the upperportion thereof also contains a similar switch S2, this portion of thefixed, waveform generator producing the treble-range waveform 13. Thisportion of the circuitry functions as follows. With switch S2 at itsneutral setting, the incoming signal traverses an incoming pathcomprising R13, R14, C7, and R16; and the feedback signal traverses afeedback path comprising C10, R17, R14, C7,, and R16. Sincecorresponding circuit elements of the input path and the feedback pathsare equal, the applied input signal is identical to the feedback signalat all frequencies. Thus, for a neutral-switch setting, the amplifier A2has a gain of zero decibels.

The Treble Circuit, Boost"-Switch Setting With switch S2 at its leftmostor boost setting," the circuit functions as follows. This switch settingshorts out R13, forming the input path S2, R14, C7, and R16 and permitsa large input signal to be applied to amplifier A2. Thus, input-pathelements R14 and C7 are placed in parallel with the bass-input paths R7,R9, C5,

and R10. This parallel arrangement causes the feedinto the relativelylow resistance of R6 of the voltage amplifier 32, rendering the effectof feedback through R17 negligible. Thus, negative feedback is appliedthrough R12, R11, C6, and R10. Therefore, for treble signals, the inputsignal is larger than the feedback signal; and the gain of amplifier A2increases with frequency from 400 to 1600 Hz, as shown at 13 of FIG. 2

The action of feedback capacitor C7, as discussed above, now produces aroll-n characteristic 14 for waveform 13. Moreover, the waveform-shapingnetwork 37 again permits unity gain at 400 Hz with the characteristicnotch, thus steepening the roll-on portion 14 in the portion of thespectrum just above 400 Hz.

The Treble Circuit, Cut-Switch Setting When switch S2 is placed in itsrightmost or cut setting, the reverse condition applies. With R17shorted out by switch S2, R141 and C7 are placed in parallel with thefeedback path R12, R11, C6, and R10. This causes the input signaltraversing R13 to be effectively shorted into the low-output impedanceof A2, rendering the effect of the input signal negligible. Thus, theinput signal is applied through R7, R9, C5, R10, and R16. The relativelylarge feedback signal and the small input signal co-act to produceminimum amplification.

As discussed above, the action of feedback capacitor C7 produces aroll-on characteristic. Moreover, the waveform-shaping network 37 againpermits unity gain at 400 Hz with the characteristic notch, thussteepening the roll-on portion 14 in the portion of the spectrum justabove 400 Hz.

In the above-described manner, the fixed, waveform generator is able toproduce boosted and attenuated bass and treble waveforms each of thesebeing fixed in shape and amplitude, having a common anchoring frequency,and having substantially identical roll-off and roll-on characteristicswhose slopes average plus or minus 12 dB per octave.

The Mid-Range, Waveform Generator The discussion of FIG. 4 pointed outthat a mid-range waveform 1.8 is desirable in order to achieve selectiveresponse curves; and such a mid-range waveform may be generated by amid-range, waveform generator 39 of FIG. 8. As shown, the output fromthe fixed, waveform generator 35 is applied to the input of themidrange, waveform generator 39, the operation being as follows.

In the mid-range generator 39, R22 is a radiofrequency suppressor; R23is a return path to ground for the input electrode of amplifier A3; andC14 and C16 have negligible reactance over the audiofrequency range.

The input signal path comprises C11, R18 and C12, R20; whereas thefeedback path comprises C16, C and R21, R a potentiometer R19 beingconnected across C12 and C13. Corresponding elements of the input signalpath and of the feedback signal path are equal; and, when the slider ofpotentiometer R19 is placed at its mid-point, the feedback signal isequal to and cancels the input signal. Thus, for a mid-point setting ofpotentiometer R19, there is a unity gain for each frequency.

The Mid-Range, Waveform Generator, Boost Setting When the slider ofpotentiometer R19 is at its leftmost or boost setting, the slider of thepotentiometer picks up the full input signal, and applies it toamplifier A3 (which may be similar to those discussed above). CapacitorC11 and resistor R18 control the roll-on characteristic by allowing theinput signal to increase with increasing frequency. The boost setting ofpotentiometer R19 permits the full-bridged-tee configuration comprisingR19, R20, C12 and C13 to become part of the feedback path; so thatmaximum feedback signal is attenuated at the anchoring frequency,displaying the characteristic peak at 400 Hz of FIGS. 4 through 7.

The Mid-Range, Waveform Generator, Cut Setting When the slider of thepotentiometer R19 is at its rightmost or cut setting, the slider of thepotentiometer picks up the full feedback signal, and applies it toamplifier A3. C15 and R21 control the roll-off portion by allowing thefeedback signal to increase with increasing frequency.

With the slider of potentiometer R19 at its cut setting, theabove-described, full-bridged tee (R19, R20, C12, and C13) becomes partof the input signal path; so that maximum input signal is attenuated atthe anchoring frequency.

Thus, the mid-range waveform 18 of FIGS. 4 7 has a roll-on portion, aroll-off portion, and a peak (and notch) at the anchoring frequency.

The Mid-Range, Waveform Generator, Variable The above explanation hasindicated how the midrange, waveform generator 39 is capable ofproducing a positive, amplified, mid-range waveform 18; and a negative,attenuated, mid-range waveform 18. Since these waveforms 18 are obtainedby extreme settings of potentiometer R19, it will be readily apparentthat intermediate potentiometer settings will generate a family ofmid-range waveforms, indicated by the dotted lines of FIG. 10. Thus, thevariable, mid-range, waveform generator is capable of selectivelyamplifying the mid-range waveform while substantially maintaining thepositioning of the mid-range waveform, this amplification beingidependent of the lower-range and upper-range waveforms.

Variable, Waveform Generator As indicated in the introductory passages,it is often desirable for the musician to be able to change not only thetype of notes produced by the sound system but to also be able to changethe amplitude of these various notes, and the relative response of theirharmonics.

FIG. 8 shows a variable, waveform generator 41 that is substantially thesame as the fixed, waveform generator 35 previously discussed thedifference being that the variable, waveform generator 41 usespotentiometers R26 and R29 instead of the switches S1 and S2,respectively.

The operation of the variable, waveform generator 41 is substantiallythe same as that of the fixed, waveform generator 35; that is, when thepotentiometers R26 and/or R29 are at their extreme leftmost or rightmostsettings, the variable, waveform generator 41 produces substantially thesame fixed waveforms 11 and 13 previously discussed. However, as thepotentiometers R26 and R29 are placed at intermediate settings, theresultant waveforms have their amplitudes and shapes varied to produce afamily of waveforms, indicated by the dotted lines of FIG. 11. Thesolid-line representations l1 and 13 indicate the previouslydiscussed,fixed waveforms, these forming the envelope of the family of curves.

Thus, the variable, waveform generator 41 is able to produce any of thefamily of waveforms indicated in this way, selectively amplifying thelower-range and/or the upper-range waveforms while substantiallymaintaining the anchoring frequency.

Combination of Waveforms The disclosed circuitry is such that thevarious waveforms may be selectively combined; that is, certainwaveforms may be amplified, other waveforms may be attenuated, stillother waveforms may be left untouched and all of these waveforms may beadded together algebraically. That is, the attenuated portions may besubstracted from the amplified portions and vice versa to provide aplurality of response curves of various shapes. In fact, when themaximal output of the fixed waveform generator is added to the maximaloutput of the variable, waveform generator, the overall response curvemay have an amplitude that may be twice as large as either; andcombinations and adjustmerits of these two waveforms with the mid-rangewaveform can produce response curves that may vary from a positive,double-amplitude to a negative, double-amplitude, composite, waveform.

The volume control 42 adjusts the ultimate amplitude of the composite,response curve.

Throughout this discussion, resistors R8, R20, and R25 of the fixed,waveform generator 35; the mid range, waveform generator 39', and thevariable, waveform generator 41; respectively, are shown to be of fixedvalue. However, these resistors may be replaced by variable resistancesfor external controls to give sharper or flatter roll-on and roll-offportions than displayed in FIGS. 2 -7 and FIGS. 10 and 11. Thismodification would be advantageous in that the musician would be allowedeven greater control over the coloring of his sound.

Pre-Amplifier The term pre-amplifier" is frequently applied to acombination of electronic devices such as the input network 30; thefixed, waveform generator 35; the midrange, waveform generator 39; andthe variable, waveform generator 41. In general, a pre-amplifier despiteits discussed amplification handles only smallmagnitude, electricalsignals; and may, therefore, be made quite small. As a result, such apre-amplifier may be made as a small, separate unit; and, when sodesired, may be physically positioned at a location that is differentfrom the rest of the apparatus. This will be discussed later.

The Power Amplifier As discussed above, the pre-amplifier produces arelatively-low-amplitude, composite, electrical, output signal thatcorresponds to the desired response curve; but, in order to produce anappreciable volume that may be heard by a large audience, the output ofthe preamplifier must be further amplified and such furtheramplification is generally achieved by means of a power amplifier. Sucha power amplifier, 44, is shown in FIG. 8. Here, the composite outputfrom the pre-amplifier is applied to the input of power amplifier 44which may take any of a number of forms. In the illustration, the inputstage of the power amplifier 44 comprises a differential amplifier madeup of two transistors, Q1 and Q2, the output of the differentialamplifier being applied to a transistor Q3 that, in turn, drives twosets of cascaded transistors Q4, Q5, Q6 and Q7, Q8, Q9 this arrangementbeing desirable to avoid overloading and distortion. Negative feedbackis applied from the amplifier output to the base of Q2 (noninvertinginput) via R40. The composite output of the two sets of transistors isapplied to one or more output jacks J3 and J4, which receive the plugsfrom suitable loudspeakers.

It has been found that transistorized circuits are unable to withstandshort circuits or prolonged overloads, so a protective, current-limitingcircuit is incorporated into the circuit of the power amplifier 44 toprotect it against momentary overloads or short circuits.

It will be noted that transistor Q7 is driven by a current source formedby R44, R45, and C28; and that transistor O4 is driven by a currentsource formed by R46, R47, and C29. For excessive, positive, currentpeaks, diodes D2 act to shunt the excessive current away from the baseelectrode of Q7; whereas, for excessive, negative, current peaks, diodesD3 and D4 act to shunt the excessive current away from the baseelectrode of Q4. In this way, symmetrical, positive and negative,current limiting is achieved for excessive currents ranging fromoverloads to short circuits.

The disclosed protection circuitry is important, for the safety oftransistors Q4 Q9, and also since the power supply is all solid statefor avoiding unbalanced currents in transformer T2. Moreover, thedisclosed current-limiting arrangement obviates the need for a powershut-down circuit such a shut-down circuit being inadvisable, since itstransient spikes produce unacceptable sound-quality deterioration. Afuse F1 protects the circuit against prolonged short circuits andoverloads.

In this way, the output signal from the power amplifier corresponds tothe desired response curve, as determined by the settings of the variouscontrols of the pre-amplifier, and has the desired power to energize theloudspeakers.

The Power Source It is well know that active electronic devices, such astransistors, require a so-called DC power source which is mostconveniently obtained from a converter that converts thereadily-available, 60-I-Iz power to the desired DC. Such a converter 46is shown in FIG. 8. As indicated, the converter receives AC power, adouble-pole, reversing switch S3 being used to assure minimal hum. TheAC power traverses a fuse F1; and a suitable pilot lamp L1 is used toindicate when the circuit is energized. The 60-Hz, AC power is thenapplied to a full-wave rectifier D1 1 -D14 that provides a DC voltagethat energizes an oscillator comprised of transistors Q10 and Q11. Thisoscillator produces a square-output waveform of a very high frequencytypically 30,000 Hz. This very-highoscillation frequency has beenselected in order to provide minimal audio interference, since itsfrequency is ultrasonic i.e., well above the highest frequency heard bythe human ear. Thus, these ultrasonic oscillations do not produce anysound that may disturb the listener or the musician, in live performanceor in a recording studio.

In the present case, it is desirable that the oscillator begin operationimmediately, and continue to oscillate; and this result is assured bythe use of two trigger-pulse generators comprising, respectively, R58,C33, D15 and R59, C34, D16. The operation of these triggerpulsegenerators is such that each periodically produces an individual triggerpulse that is applied to respective bases of the transistor Q and Q11 ofthe oscillator. Thus, each trigger-pulse generator periodically triggersits associated transistor into operation; so that the oscillatorimmediately begins its operation, and continues its oscillation.

In order to further assure immediate and continuous operation of theoscillator, each of the trigger-pulse generators has a frequency that isslightly different from the other; and neither of these is a multiple ofthe frequency of the oscillator i.e., all three are nonsynchronous. Suchanon-synchronous arrangement assures that the oscillator will not belocked out; it will always receive effective trigger pulses.

The output of the oscillator is, in turn, applied to a second, full-waverectifier D7 -D10 that converts the ultrasonic, oscillator output toanother DC voltage, transformers T1 and T2 improving the efficiency.Since the disclosed circuitry requires two different DC voltages, the DCoutput from the second, full-wave rectifier D7 D10 is applied to asmoothing-and-filtering network that provides a first, i- 38-volt, DCsource; and a second, i -volt, DC source these different DC voltages Band V being applied to the power amplifier and to the pre-amplifier,respectively.

Packaging FIG. 12 illustrates a typical packaging of the disclosedapparatus, the cabinet having been designed to act as a base for thevarious electronic components, and to act as a heat sink that dissipatesthe heat into the air. One early model was about eleven inches long,about three inches high, about seven inches deep, weighed about fivepounds, and had a power rating of about one-hundred watts RMS, into fourohms.

The left side of the cabinet has a power cord for plugging into a wallreceptacle; and has an on-off power switch $3, a pilot light L1, and afuse F1. The left side of the cabinet also contains two output jacks, J3and J4.

The front of the cabinet has the operating controls, namely: two inputjacks J1 and J2; a distortion control R5; a first, three-position switchS1 for the bass-range, fixed, waveform generator; a second,three-position switch S2 forthe treble-range, fixed, waveform generator;a first control R26 for the bass-range, variable, waveform generator; asecond control R29 for the treble-range, variable, waveform generator; acontrol R19 for the mid-range, variable, waveform generator; and avolume control 42.

In use, the apparatus of FIG. 12 is electrically connected between themusical instrument and the loudspeakers by means of the various jacksand plugs; and the unit is then placed conveniently for the musician whomay then adjust the various controls to his satisfaction relative to theinstrument, the accoustics of the area, the type of musical number, theaudience, etc.

As indicated above, the pro-amplifier of FIG. 8 may be made small enoughto be placed in the body of the guitar; and some musicians prefer thislocation, as they may then make the various adjustments unobtrusivelyeven during the performance of a musical selection. In this case, theinstallation would appear as indicated in FIG. 1, this illustrationshowing a guitar with a preamplifier located within the guitar body.

Where desired, the entire apparatus may be incorporated into the speakerenclosure. Due to the tremendous reduction in size and weight overpresent-day systems, the entire package may be incorporated into anappropriately hollowed out solid-body or hollow-body guitar.Alternatively, it may be incorporated into an electric piano, anelectric organ, etc. All or part of the disclosed system may also beapplied to Hi Fi, tape recorders, cassettes, television, automobileentertainment systems, etc.

It will be realized that the disclosed system requires only one channelfor any instrument; whereas, prior-art systems often required basschannels, treble channels, etc.

Moreover, the amount of amplification and/or attenuation is readilycontrolled by the musician, who may choose to strongly emphasize thebass tones, emphasize the treble tones, and/or mix in small amounts ofintermediate tones. In this way, the musician has complete control overthe tone produced by his instrument; and, since the disclosed amplifieris capable of producing over one-hundred watts, the musician does notneed the prior-art, electronic, sound system with its built-inshortcomings.

Distortion Control In the past, if a guitarist desired to practice amusical selection that required the distortion discussed above, thismeant that he had to turn the volume control up to its maximal setting;and this tended to disturb everyone in the neighborhood. The disclosedinvention permits this type of distortion practice without the prior-artdisturbance, by using the following technique.

The volume control 42 is first turned down to provide a minimal volumeof sound; and the distortion control R5 is then turned up until thedesired distortion is obtained. At this time, the volume control isreadjusted. The distortion control and the volume control are thussubstantially independent of each other.

in this way, the desired amount of distortion is obtained; but theoverall volume of sound is low enough not to cause any disturbance.

SUMMARY The disclosed invention has many advantages over prior-artarrangements. First of all, the disclosed apparatus provides new, livesound that thrills musicians. The new, live sound is achieved byselectable use of controllable, bass-range waveforms, treble-rangewaveforms, and mid-range waveforms. The ultimate sound is totally underthe control of the musician. A separate distortion control is provided.A separate volume control is provided. Distortion effects may bepracticed without undue disturbances. The apparatus is designed towithstand momentary short circuits. Thus, it provides a versatile,solid-state, musical apparatus having superior sound, combined withsmall size and light weight.

I claim:

1. Apparatus for performing a filtering and selective amplifyingfunction on an applied waveform or signal having a particular frequencyrange to produce a response curve having a given frequency spectrum,comprising:

means for generating a lower-range waveform having a roll-off portionthat is anchored at a given anchoring frequency, and for independentlyand selectively amplifying said lower-range waveform while substantiallymaintaining said anchoring frequency; said roll-off portion having arelatively-steep configuration;

means for generating an upper-range waveform having a roll-on portionthat is anchored at substantially said anchoring frequency, and forindenpendently and selectively amplifying said upper-range waveformwhile substantially maintaining said anchoring frequency;

said roll-on portion having a relatively-steep configuration;

means for combining said lower-range waveform and said upper-rangewaveform to produce said desired response curve;

said response curve having a peak-shaped notch that is substantiallycentered at said anchoring frequency.

2. The invention of claim 1, wherein said anchoring frequency issubstantially 400 Hz. I

3. The invention of claim 1, wherein said selective amplificationincludes positive and negative amplification.

4. The invention of claim 1, including means for independentlydistorting said response curve.

5. The invention ofclaim 1, including means for distorting said responsecurve, and means for controlling the ultimate amplitude of said responsecurve.

6. The invention of claim 1, wherein said means for generating saidlower-range waveform comprises a fixed waveform generator.

7. The invention of claim 1, wherein said means for generating saidlower-range waveform comprises a variable waveform generator.

8. The invention of claim 1, wherein said means for generating saidlower-range waveform comprises a fixed waveform generator and a variablewaveform generator;

means for combining the outputs of said fixed and variable waveformgenerators for producing said response curve.

9. The invention of claim 1, wherein said means for generating saidupper-range waveform comprises a fixed waveform generator.

10. The invention of claim 1, wherein said means for generating saidupper-range waveform comprises a variable waveform generator.

11. The invention of claim 1, wherein said means for generating saidupper-range waveform comprises a fixed waveform generator and a variablewaveform generator;

means for combining the outputs of said fixed waveform generator andsaid variable waveform generator to produce said response curve. 12. Theinvention of claim 1, wherein:

said means for generating said lower-range waveform comprises a fixedwaveform generator and a variable waveform generator;

said means for generating said upper-range waveform comprises a fixedwaveform generator and a variable waveform generator;

means for combining the outputs from said fixed and said variablewaveform generators.

13. The invention of claim 1, wherein said roll-off portion of saidlower-range waveform has an original slope of about twelve decibels peroctave.

14. The invention of claim 1, wherein said roll-on portion of saidupper-range waveform has an original slope of about twelve decibels peroctave.

15. The invention of claim I, wherein said roll-off portion of saidlower-range waveform is substantially similar to said roll-on portion ofsaid upper-range waveform.

16. The invention of claim 1, including means for generating apeak-shaped, mid-range waveform having its peak positioned atsubstantially said anchoring frequency;

means for independently and selectively amplifying said mid-rangewaveform while substantially maintaining said positioning of saidmid-range waveform.

17. The invention of claim 16, wherein said peakshaped, mid-rangewaveform is shaped substantially similarly to said notch of saidresponse curve.

18. The invention of claim 17, including means for combining saidmid-range waveform with said lowerrange waveform and said upper-rangewaveform.

19. The invention of claim 18, wherein said waveform-generating meanscomprises electronic circuits.

20. The invention of claim 19, including a power amplifier having adual-clipping, safety action;

said dual-clipping, safety action comprising means for clipping both thepositive-going and the negative-going waveforms of said power amplifier.

21. Apparatus for performing a filtering and selective amplifyingfunction on an applied waveform or signal having a particular frequencyrange to produce a musical-instrument response curve having a givenfrequency spectrum, comprising:

means, comprising a fixed waveform generator and a variable waveformgenerator, for generating a lower-range waveform having a roll-offportion that is anchored at a given anchoring frequency, and forindependently and selectively amplifying said lower-range waveform whilesubstantially maintaining said anchoring frequency;

said roll-off portion having a relatively-steep configuration;

means, comprising a fixed waveform generator and a variable waveformgenerator, for generating an upper-range waveform having a roll-onportion that is anchored at substantially said anchoring frequency, andfor idependently and selectively amplifying said upper-range waveformwhile substantially maintaining said anchoring frequency;

said roll-on portion having a relatively-steep configuration;

said response curve having a peak-shaped notch that is substantiallycentered at said anchoring frequency;

means for generating a peak-shaped, mid-range waveform having its peakpositioned at substantially said anchoring frequency, and forindependently and selectively amplifying said mid-range waveform whilesubstantially maintaining said positioning of said mid-range waveform;

said peak-shaped, mid-range waveform being shaped substantiallysimilarly to said notch of said response curve; and

means for combining the outputs from said waveform generators.

plitude of said response curve.

1. Apparatus for performing a filtering and selective amplifyingfunction on an applied waveform or signal having a particular frequencyrange to produce a response curve having a given frequency spectrum,comprising: means for generating a lower-range waveform having aroll-off portion that is anchored at a given anchoring frequency, andfor independently and selectively amplifying said lower-range waveformwhile substantially maintaining said anchoring frequency; said roll-offportion having a relatively-steep configuration; means for generating anupper-range waveform having a roll-on portion that is anchored atsubstantially said anchoring frequency, and for indenpendently andselectively amplifying said upper-range waveform while substantiallymaintaining said anchoring frequency; said roll-on portion having arelatively-steep configuration; means for combining said lower-rangewaveform and said upperrange waveform to produce said desired responsecurve; said response curve having a peak-shaped notch that issubstantially centered at said anchoring frequency.
 2. The invention ofclaim 1, wherein said anchoring frequency is substantially 400 Hz. 3.The invention of claim 1, wherein said selective amplification includespositive and negative amplification.
 4. The invention of claim 1,including means for independently distorting said response curve.
 5. Theinvention of claim 1, including means for distorting said responsecurve, and means for controlling the ultimate amplitude of said responsecurve.
 6. The invention of claim 1, wherein said means for generatingsaid lower-range waveform comprises a fixed waveform generator.
 7. Theinvention of claim 1, wherein said means for generating said lower-rangewaveform comprises a variable waveform generator.
 8. The invention ofclaim 1, wherein said means for generating said lower-range waveformcomprises a fixed waveform generator and a variable waveform generator;means for combining the outputs of said fixed and variable waveformgenerators for producing said response curve.
 9. The invention of claim1, wherein said means for generating said upper-range waveform comprisesa fixed waveform generator.
 10. The invention of claim 1, wherein saidmeans for generating said upper-range waveform comprises a variablewaveform generator.
 11. The invention of claim 1, wherein said means forgenerating said upper-range waveform comprises a fixed waveformgenerator and a variable waveform generator; means for combining theoutputs of said fixed waveform generator and said variable waveformgenerator to produce said response curve.
 12. The invention of claim 1,wherein: said means for generating said lower-range waveform comprises afixed waveform generator and a variable waveform generator; said meansfor generating said upper-range waveform comprises a fixed waveformgenerator and a variable waveform generator; means for combining theoutputs from said fixed and said variable waveform generators.
 13. Theinvention of claim 1, wherein said roll-off portion of said lower-rangewaveform has an original slope of about twelve decibels per octave. 14.The invention of claim 1, wherein said roll-on portion of saidupper-range waveform has an original slope of about twelve decibels peroctave.
 15. The invention of claim 1, wherein said roll-off portion ofsaid lower-range waveform is substantially similar to said roll-onportion of said upper-range waveform.
 16. The invention of claim 1,including means for generating a peak-shaped, mid-range waveform havingits peak positioned at substantially said anChoring frequency; means forindependently and selectively amplifying said mid-range waveform whilesubstantially maintaining said positioning of said mid-range waveform.17. The invention of claim 16, wherein said peak-shaped, mid-rangewaveform is shaped substantially similarly to said notch of saidresponse curve.
 18. The invention of claim 17, including means forcombining said mid-range waveform with said lower-range waveform andsaid upper-range waveform.
 19. The invention of claim 18, wherein saidwaveform-generating means comprises electronic circuits.
 20. Theinvention of claim 19, including a power amplifier having adual-clipping, safety action; said dual-clipping, safety actioncomprising means for clipping both the positive-going and thenegative-going waveforms of said power amplifier.
 21. Apparatus forperforming a filtering and selective amplifying function on an appliedwaveform or signal having a particular frequency range to produce amusical-instrument response curve having a given frequency spectrum,comprising: means, comprising a fixed waveform generator and a variablewaveform generator, for generating a lower-range waveform having aroll-off portion that is anchored at a given anchoring frequency, andfor independently and selectively amplifying said lower-range waveformwhile substantially maintaining said anchoring frequency; said roll-offportion having a relatively-steep configuration; means, comprising afixed waveform generator and a variable waveform generator, forgenerating an upper-range waveform having a roll-on portion that isanchored at substantially said anchoring frequency, and for idependentlyand selectively amplifying said upper-range waveform while substantiallymaintaining said anchoring frequency; said roll-on portion having arelatively-steep configuration; said response curve having a peak-shapednotch that is substantially centered at said anchoring frequency; meansfor generating a peak-shaped, mid-range waveform having its peakpositioned at substantially said anchoring frequency, and forindependently and selectively amplifying said mid-range waveform whilesubstantially maintaining said positioning of said mid-range waveform;said peak-shaped, mid-range waveform being shaped substantiallysimilarly to said notch of said response curve; and means for combiningthe outputs from said waveform generators.
 22. The invention of claim21, wherein said roll-off portion of said lower-range waveform issubstantially similar to said roll-on portion of said upper-rangewaveform.
 23. The invention of claim 21, including means forindependently distorting said response curve, and means forindependently controlling the ultimate amplitude of said response curve.